System for server obtaining terminal address via searching address table or via broadcasting to all terminals through exchange in response to terminal address interrogation request

ABSTRACT

A originating terminal sends an ATM address interrogation request to a server if the ATM address of another party&#39;s terminal is unknown at the time of communication. Upon receiving the ATM address interrogation request from the terminal, the server refers to an ATM address table, searches the table for an ATM address corresponding to a protocol address contained in the interrogation request and notifies the originating terminal of this ATM address. If an ATM address corresponding to the protocol address has not been registered in the ATM address table, the server transfers (broadcasts) the ATM address interrogation request to all terminals. The server notifies the originating terminal of an ATM address obtained by an answer in response to this interrogation request and registers the ATM address in the ATM address table.

BACKGROUND OF THE INVENTION

This invention relates to a communication system such as an ATM-LAN, aserver and an address management method. More particularly, theinvention relates to a communication system equipped with a plurality ofterminals, a server having an ATM address table for storing thecorresponding relationship between the protocol address and ATM addressof each terminal, and an ATM exchange which accommodates each terminaland the server.

Improvements in the performance of personal computers and work stationshave been accompanied by the rapid proliferation of applications fordealing with high-speed data and multimedia. In addition, suchtechniques as remote file access and decentralized computing have beenestablished though use of LANS. For these reasons, there is expected tobe greater demand for higher speed LANs for multimedia purposes.

In order to satisfy these expectations, there has been increasedactivity in the research and development of LANs (ATM-LANs) using ATMcommunication. An ATM-LAN is a switching LAN in which terminals areconnected in a star-like configuration to an apparatus (an ATM exchange,for example) having an ATM switching function. Each terminal establishesa virtual channel (VC) directed toward a destination terminal andperforms a data transmission by means of a fixed-length packet, referredto as an ATM cell, comprising a five-byte header and 48-byte data. As aresult, it is possible to set a number of VCs on a terminal interface(where the number is capable of being expressed by the VPI/VCI) so thatthe terminal is capable of communicating with a plurality of otherterminals simultaneously via the set VCs.

When communication is performed on a LAN, it is generally required thatthe originating terminal know the physical address of the terminal ofthe other party. In a conventional LAN, the physical address is a MACaddress. Data in a LAN is transmitted in frame units, with each framecontaining the addresses of the originating and terminating terminals.FIG. 21 is a diagram of a frame in a case where the protocol of a LAN isTCP/IP. The frame includes a start delimiter (SD) and an end delimiter(ED) between which are placed a destination address DA serving as acontrol field and a layer-2 address (MAC address), a sending address SA,an information field I (IP packet) and a frame scanning sequence FSC.The IP packet is subdivided into a control information field, adestination address DA′ serving as a protocol address (IP address), asending address SA′ and an information field I′.

Communication with another terminal is not possible if the MAC addressof the terminal is not known. If the MAC address of a party's terminalis unknown (but the protocol address is known), therefore, the originalterminal determines the MAC address of the higher-order protocol address(IP address) by an address resolution protocol (ARP) and performscommunication upon disassembling the higher-order packet (IP packet)into frames using the MAC address.

FIG. 22 is a processing flowchart of the ARP. If the MAC address ofanother party's terminal is unknown (NO at step S1), the originatingterminal creates a frame (ARP frame) and sends the frame to the LAN(step S2). The ARP frame contains {circle around (1)} a broadcastaddress as the destination MAC address DA of the frame, {circle around(2)} a protocol address of another party's terminal serving as thedestination protocol address DA′, and {circle around (3)} an indicationthat the frame is an ARP frame, this serving as control information CF′.

Upon receiving this ARP frame, each terminal determines whether theframe has its own address or is a broadcast frame. In this case, theframe is a broadcast frame and therefore the frame is accepted (stepS11). Next, after verification of the fact that the frame is an ARPframe, each terminal determines whether the protocol address of thedestination agrees with its own protocol address (step S12). Processingis terminated if the two addresses disagree. If the two addresses doagree, however, an answer frame which contains the terminals own MACaddress is created at sent back to the originating terminal (step S13).Upon receiving the answer frame (YES at step S3), the originatingterminal registers the correspondence between the MAC address of theother party's terminal contained in this answer frame and the protocoladdress in an internal IP-MAC address table (step S4) and then creates aframe (see FIG. 21) using the other party's MAC address and sends thisframe to the LAN to perform LAN communication (step S5).

The foregoing is for the case of connection-less communication. In anATM-LAN based upon connection-type communication, a VC is establishedbetween terminals and communication is performed while forming ahigher-order packet into cells. In such an ATM-LAN, a physical addresscorresponds to the address (VPI/VCI) of the ATM layer, and this ATMlayer address (VPI/VCI) is decided by a set-up sequence using the ATMaddress of the terminal. A set-up sequence is a call set-up processingsequence executed at the time of an outgoing call.

Thus, when the ATM address of the other party's terminal is unknown inan ATM-LAN, communication cannot be performed. This necessitates amethod of analyzing the ATM address based upon the higher-order protocoladdress.

Conventional methods of acquiring the ATM address of another party'sterminal include a broadcast method of broadcasting an interrogationrequest to all terminals and a server method of providing a serverwithin the ATM-LAN and interrogating the server.

FIG. 23 is a diagram for describing the broadcast method. Terminals 1a,1b, 1c are connected to an ATM-LAN 2. According to the broadcast method,the ATM address interrogation request is broadcast within the network ifthe ATM address of the other party's terminal is unknown at the moment acommunication request is generated, and a prescribed terminal respondsto this interrogation by answering with its own ATM address. Forexample, if the ATM address of terminal 1b is unknown to the terminal 1awhen this terminal communicates with the terminal 1b in FIG. 23, theterminal 1a broadcasts an ATM address interrogation request cell (whichhas the protocol address of terminal 1b) within the network. Theterminal 1b, which is that terminal having a protocol address identicalwith that contained in the received cell, answers the terminal 1a withits own ATM address. The terminal 1a uses the received ATM address tocall the terminal 1b and communicate with it.

FIG. 24 is a diagram for describing the server method. FIG. 24 shows theterminals 1a, 1b, 1c and the ATM-LAN 2, which in this case is providedwith a server 3. According to the server method, the correspondingrelation between protocol addresses and ATM addresses of all terminalsis registered in an ATM address table in advance. If the ATM address ofanother party's terminal is unknown at the moment a communicationrequest is issued, an ATM address interrogation request is sent to theserver and the server answers by retrieving the ATM address from the ATMaddress table. For example, if the ATM address of terminal 1c is unknownto the terminal 1a when this terminal communicates with the terminal 1cin FIG. 24, the terminal 1a sends the server 3 an ATM addressinterrogation cell (which has the protocol address of terminal 1c). Theserver 3 answers the terminal 1a by retrieving the ATM address ofterminal 1c from the ATM address table, and the terminal 1a uses thereceived ATM address to call the terminal 1c and communicate with it.

If the ATM address of another party's terminal is unknown at the momenta communication request is issued in the broadcast method, a broadcastis made within the network and the terminal is interrogated directly.Unlike the server method, implementation is easy because it isunnecessary to create a data base in advance. However, in cases wherefrequent communication is made with an unspecified terminal whose ATMaddress is unknown, broadcast of the interrogation request is madewhenever a communication request is issued. A problem which arises as aconsequence is an increase in control traffic. This problem becomesparticularly pronounced with an increase in the number of terminals ordepending upon the scale of the network.

With the server method, on the other hand, there is no increase intraffic because there is no broadcast of an interrogation request.However, it is required that information (the correlation betweenprotocol addresses and ATM addresses) regarding all terminals connectedto the ATM-LAN be registered in the ATM address table in advance. At thetime of initial installation therefore, it is necessary that theinformation regarding all terminals be registered in a data base (ATMaddress table) and that the data base be updated whenever a terminal isadded on or moved. Further, an increase in the number of terminals or anincrease in the scale of the network necessitates a data base of alarger capacity. This leads to an increase in the scale of the serverhardware.

SUMMARY OF THE INVENTION

Accordingly, a first object of the present invention is to provide acommunication system such as an ATM-LAN, a server and an addressmanagement method whereby the problems of the aforementioned methods aremitigated using the server method and broadcast method in combination.

A second object of the present invention is to provide a communicationsystem such as an ATM-LAN, a server and an address management method inwhich an increase in traffic can be suppressed.

A third object of the present invention is to provide a communicationsystem such as an ATM-LAN, a server and an address management method inwhich an initial setting or updating of an address table (data base) isnot necessary at the time of initial installation or whenever a terminalis added on or moved.

A fourth object of the present invention is to provide a communicationsystem such as an ATM-LAN, a server and an address management method inwhich a large-capacity data base is not required, thus making itpossible to reduce the scale of server hardware.

In accordance with the present invention, the foregoing objects areattained by providing an address management method comprising a firststep in which an originating terminal sends a terminal addressinterrogation request to a server if the terminal address of anotherparty's terminal is unknown at the time of communication, a second stepin which the server, upon receiving the terminal address interrogationrequest from the terminal, refers to an address table and searches for aterminal address corresponding to a protocol address contained in theinterrogation request, a third step in which, if a terminal addresscorresponding to the protocol address is obtained from the addresstable, the server notifies the terminal of this terminal address, afourth step in which, if the terminal address is not obtained from theaddress table, the server transfers the terminal address interrogationrequest containing the protocol address to all terminals via anexchange, a fifth step in which, when each terminal receives theterminal address interrogation request transferred from the server, theterminal determines whether the protocol address contained in theinterrogation request agrees with its own protocol address and notifiesthe server of its own terminal address if agreement is achieved, and asixth step in which the server notifies the originating terminal of theterminal address of which it has been notified.

Further, according to the present invention, the foregoing objects areattained by providing a communication system equipped with a pluralityof terminals, a server having an address table for storing thecorresponding relationship between a protocol address and terminaladdress of each terminal, and an exchange which accommodates eachterminal and the server, wherein (1) each terminal includes means forsending a terminal address interrogation request to the server if theterminal address of another party's terminal is unknown at the time ofcommunication, communication means for communicating with the otherparty's terminal via the exchange using a terminal address of which ithas been notified by the server in response to the interrogationrequest, and terminal address answering means for answering the serverwith its own terminal address if a protocol address contained in aterminal address interrogation request transferred from the serveragrees with its own protocol address, and (2) the server includes meansfor referring to the address table and searching for a terminal addresscorresponding to a protocol address contained in a terminal addressinterrogation request from a terminal, means which, if a terminaladdress corresponding to the protocol address has not been registered inthe address table, is for transferring the terminal addressinterrogation request containing this protocol address to all terminalsvia the exchange, and means for notifying the terminal which has issuedthe interrogation request of a terminal address obtained from theaddress table or of a terminal address obtained by an answer from aterminal.

Furthermore, in accordance with the present invention, the foregoingobjects are attained by providing a server comprising an address tablefor storing the corresponding relationship between a protocol addressand terminal address of each of a plurality of terminals, search meansfor referring to the address table and searching for a terminal addresscorresponding to a protocol address contained in a terminal addressinterrogation request from a terminal, and interrogation means which, ifa terminal address corresponding to the protocol address has not beenregistered in the address table, is for interrogating all terminals, viaan exchange, for the terminal address corresponding to this protocoladdress, wherein in response to receipt of a terminal addressinterrogation request from an originating terminal, the search meansrefers to the terminal address table to obtain the terminal addressconforming to the protocol address contained in this terminal addressinterrogation request and, if this terminal address has not beenregistered, the interrogation means interrogates all the terminal forterminal address.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram for describing the principles of the presentinvention;

FIG. 2 is a diagram showing the configuration of an ATM-LAN according tothe present invention;

FIG. 3 is a diagram showing an ATM address table according to thepresent invention;

FIGS. 4A, 4B, are diagrams showing the constitution of an ATM cell;

FIG. 5 is a diagram showing the detailed constitution of an ATM cell towhich a tag has been added;

FIG. 6 is a table for describing the relationship between taginformation and outgoing lines;

FIG. 7 is a diagram for describing an ATM switch;

FIG. 8 is diagram showing a simplified representation of the ATM switch;

FIG. 9 is a diagram for describing broadcast of an ATM-ARMARP request;

FIG. 10 is a diagram useful in describing control of sending receivingof an ATM-ARP message;

FIG. 11 is a diagram (part 1) for describing a communication sequenceaccording to the present invention;

FIG. 12 is a diagram for describing the format of the ATM-ARP message;

FIG. 13 is a diagram (part 2) for describing the communication sequenceaccording to the present invention;

FIG. 14 is a flowchart of processing executed by an originating terminalwhen a communication request is issued;

FIG. 15 is a flowchart of processing executed by terminating terminalwhen an ATM-ARP request is received;

FIG. 16 is a flowchart of processing executed by a server;

FIG. 17 is a flowchart showing ATM-ARP request transfer processing in acase where a terminal has been divided into groups;

FIG. 18 is a block diagram showing the construction of a server;

FIG. 19 is a diagram showing the construction of a terminal;

FIG. 20 is a block diagram showing the construction of a serveraccommodating section;

FIG. 21 is a diagram showing the constitution of a frame;

FIG. 22 is a flowchart of ARP processing in a LAN according to the priorart;

FIG. 23 is a diagram (according to the broadcast method) for describingconventional ARP processing in an ATM-LAN; and

FIG. 24 is a diagram (according to the server method) for describingconventional ARP processing in an ATM-LAN.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(A) Overview of the invention

FIG. 1 is a diagram for describing the principles of the presentinvention.

As shown in FIG. 1, terminals 11, 12, 13, . . . are connected to aserver 21. The terminals and the server are accommodated by an ATMexchange 31.

The terminals 11, 12, 13 have respective request generating means 11a,12a, 13a for sending an ATM address interrogation request to the server21 if the ATM address of another party's terminal is unknown at the timeof communication; answering means 11b, 12b, 13b which communicate withthe other party's terminal via the ATM exchange 31 using an ATM addressof which it has been noted by the server in response to an ATM addressinterrogation request, and answering means 11c, 12c, 13c each of whichanswers the server with its own ATM address if a protocol addresscontained in an ATM address interrogation request transferred from theserver 21 agrees with its own protocol address.

The server 21 includes an ATM address table 21a for storing, by use of alearning function, the corresponding relationship between the protocoladdress and ATM address of each terminal; search means 21b for referringto the ATM address table 21a and searching for an ATM addresscorresponding to a protocol address contained in an ATM addressinterrogation request from a terminal; broadcast means 21c which, if anATM address for which it has been interrogated is not obtained from theATM address table 21a, broadcasts an ATM address interrogation requestto all terminals via the ATM exchange 31; and answering means foranswering a terminal, which has issued the interrogation request, withthe ATM address for which it has been interrogated.

The terminal 11, which is the originating terminal, sends an ATM addressinterrogation request to the server 21 if the ATM address of anotherparty's terminal (terminal 12) is unknown at the time of communication.Upon receiving the ATM address interrogation request from the terminal11, the server 21 refers to the ATM address table 21a and searches foran ATM address corresponding to the protocol address of the terminal 12contained in the interrogation request. If an ATM address correspondingto the protocol address has been registered in the ATM address table21a, the server 21 notifies the terminal 11 of this ATM address. If anATM address corresponding to the protocol address has not beenregistered in the ATM address table 21a, however, the server 21transfers the ATM address interrogation request containing theabove-mentioned protocol address to all terminals 12, 13, . . . via theATM exchange 31. When each terminal 12, 13, . . . receives the ATMaddress interrogation request transferred from the server 21, theterminal checks to see whether the protocol address contained in theinterrogation request agrees with its own protocol address. Since theprotocol address contained in the interrogation request agrees with itsown protocol address, the terminal 12 notifies the server 21 of its ownATM address. The server 21 notifies the originating terminal 11 of theATM address of which it has been notified. As a result, the originatingterminal 11 communicates with the other party's terminal 12 via the ATMexchange 31 using the ATM address of which it has been notified by theserver 21.

Thus, if an ATM address has been registered in the ATM address table ofthe server, the ATM address can be obtained through an operation similarto that of the conventional server method in response to theinterrogation request for this ATM address. If the ATM address has notbeen registered in the ATM address table, the interrogation request forthis ATM address is broadcast to enable the ATM address to be obtained.In other words, ATM addresses are managed by making joint use of theserver method and broadcast method. This makes it possible to suppressan increase in the amount of control traffic. Moreover, ATM addressescan be perfected by successively registering correspondingrelationships, which have been found using the broadcast method, in theATM address table. In addition, it is possible to dispense with a taskfor initially setting the ATM address table and a task for updating thetable when terminals are added on or moved.

Furthermore, if all terminals are divided up into a plurality of groupsand a desired ATM address has not been registered in the ATM addresstable, the server transfers the ATM address interrogation request cellto all terminals of the first group. Monitoring is performed todetermine whether a prescribed terminal has answered with the ATMaddress within a set period of time. If notification of the ATM addressis not received within the set time period, the server transfers theinterrogation request cell to all terminals of the next group. Thus, theserver transfers the interrogation request cell while successivelychanging groups until the prescribed terminal answers with the ATMaddress. If this arrangement is adopted, there is a good possibilitythat the desired ATM address will be obtained before the interrogationrequest is sent to all terminals. As a result, any increase in trafficcan be suppressed.

Further, upon receiving notification of the desired ATM address from theprescribed terminal, the server 21 registers the correspondence betweenthe protocol address of this terminal and the ATM address of which ithas been notified in the ATM address table 21a anew. Further, the serverregisters, in the ATM address table 21a, the corresponding relationshipbetween the protocol address of the originating terminal, which addressis contained in the ATM address interrogation request received from theoriginating terminal, and the ATM address. Accordingly, if aninterrogation request for the above-mentioned ATM address is issuedafter registration, it is unnecessary to broadcast this interrogationrequest; the ATM address can be obtained in simple fashion from the ATMaddress table.

Furthermore, if the ATM address table 21a is full when the prescribedterminal has answered with the ATM address, the server 21 erases theoldest corresponding relationship referred to and newly registers thecorresponding relationship between the protocol address of the terminaland the ATM address, of which it has been notified, in the ATM addresstable. If this arrangement is adopted, a large-capacity ATM addresstable (data base) will be unnecessary and the scale of the serverhardware can be minimized. Further, by arranging is so that a terminalperiodically sends an ATM address interrogation request for its ownterminal to the server, the corresponding relationship between theterminal's own protocol address and the ATM address can be kept in theATM address table at all times.

(B) ATM-LAN of the present invention

-   -   (a) Overall configuration

FIG. 2 is a diagram showing the basic configuration of an ATM-LANaccording to the present invention.

As shown in FIG. 2, the terminals 11˜14 are connected to the server 21by respective transmission lines 41˜44 for ATM cells. The terminals andthe server are accommodated by the ATM exchange 31.

The terminals 11, 12, 13, 14 have respective request generating means11a, 12a, 13a, 14a for sending an ATM address interrogation request tothe server 21 if the ATM address of another party's terminal is unknownat the time of a communication; answering means 11b, 12b, 13b, 14b whichcommunicate with the other party's terminal via the ATM exchange 31using an ATM address of which it has been notified by the server inresponse to an interrogation request; and answering means 11c, 12c, 13c,14c each of which answers the server 21 with its own ATM address if aprotocol address contained in an ATM address interrogation requesttransferred from the server 21 agrees with its own protocol address.

The server 21 includes the ATM address table 21a for storing thecorresponding relationship between the protocol address and ATM addressof each terminal; the search/registration means 21b which, when an ATMaddress interrogation request has been received from a terminal,retrieves the ATM address corresponding to the protocol addresscontained in this interrogation request from the ATM address table 21aand registers the new corresponding relationship in the ATM addresstable 21a; the broadcast means 21c which, if an ATM address for which ithas been interrogated by a terminal is not obtained from the ATM addresstable 21a, transfers (broadcasts) an ATM address interrogation requestto all terminals via the ATM exchange 31; and the answering means foranswering a terminal, which has issued the above-mentioned interrogationrequest, with the ATM address for which it has been interrogated.

As illustrated in FIG. 3, the ATM address table 21a holds thecorresponding relationship between the protocol address and ATM addressof each terminal as well as the time at which reference was made to thecorresponding relationship. If a terminal does not know the ATM addressof another party's terminal at the time of communication, the terminalsends the server 21 an interrogation request for the ATM address. Uponreceiving the ATM address interrogation request from the terminal, thesearch/registration means 21b of the server 21 checks to determinewhether the ATM address corresponding to the protocol address containedin the request has been registered in the ATM address table 21a. If theATM address has been registered in the ATM address table 21a, thesearch/registration means 21b updates the reference time and enters theATM address into the answering means 21d. If the ATM address for whichthe server has been interrogated has not been registered kin the ATMaddress table 21a, then all terminals are interrogated to acquire theATM address. In this case, the search/registration means 21b correlatesthe acquired ATM address and the reference time with the protocoladdress and stores this in the ATM address table 21a.

With reference again to FIG. 2, the ATM exchange 31 includes an ATMswitch 32, terminal accommodating sections 33a˜33d and a serveraccommodating section 34. The terminal accommodating sections 33a˜33dadd a tag (routing information) onto a cell entered from the respectiveterminal, replaces the VPI/VCI and sends the result to the ATM switch32. Further, the terminal accommodating sections 33a˜33d remove the tagfrom a cell entered from the ATM switch 32 and then sends the cell tothe respective one of the transmission lines 41˜44. The serveraccommodating section 34 adds a tag (routing information) onto a cellentered from the server 32, replaces the VPI/VCI and sends the result tothe ATM switch 32. Further, the server accommodating section 34 removesthe tag from a cell entered from the ATM switch 32 and then sends thecell to the server 21.

-   -   (b) ATM cell

As shown in FIG. 4A, an ATM cell is composed of a 53-byte, fixed-lengthblock in which five bytes constitute a header HD and the remaining 48bytes constitute an information field (payload) DT. The header HDcontains a virtual channel identifier (VCI) for call identification soadapted that a destination can be ascertained even after data is brokendown into blocks; a virtual path identifier (VPI) for specifying a path;a generic flow control (GFC) used to control flow between links; payloadtype (PTI); a cell loss priority (CLP) and a header error control (HEC),which is a code for header error revision. Before this ATM cell is fedinto the ATM switch 32, the terminal accommodating sections 33a˜33d addon a one-byte routing tag TAG and update the VPI/VCI, as shown in FIG.4B.

-   -   (c) Operation when ATM address of other party's terminal is        already known

Assume by way of example that an operation is performed in whichterminal (originating terminal) 11 calls terminal (terminating terminal)13. (This is an operation for entering the ATM address of theterminating terminal 13.) A cell assembler within the originatingterminal divides a set-up message (data which includes the ATM addressof the original terminal and the ATM address of the terminatingterminal, etc.) into cell units, adds a signaling VCI onto each item ofdivided data to generate a signal cell and sends the signal cell to theATM exchange 31. If a signal device (not shown) in the ATM exchange 31receives the signal cell, the device assembles the information containedin the signal cell and sends the information to a CPU (not shown). Onthe basis of the received message, the CPU performs call processingcontrol, decides the VPI/VCI and assigns a prescribed VCI to theoriginating terminal and terminating terminal.

The CPU of the ATM exchange 31 correlates the VCI of the originatingterminal 11 with a routing table within the terminal accommodatingsection 33a and registers information (tag information) specifying theoutgoing line of the cell having this VIC as well as a VPI/VCI forreplacement.

When a path is formed between the originating terminal 11 andterminating terminal 13, the originating terminal 11 disassembles thedata to be transmitted into prescribed byte lengths, creates a cell uponadding on a header containing the assigned VCI mentioned above and sendsthe cell to the ATM exchange 31. When the cell enters from the terminal11 via a prescribed incoming highway (in-line) 41, the terminalaccommodating section 33a of the ATM exchange 31 adds on the taginformation TAG (see FIG. 4B) upon referring to the routing table andsends the result to the ATM switch 32 upon replacing the VPI/VCI. On thebasis of the tag, the ATM switch 32 sends the ATM cell to a prescribedoutgoing highway (out-line) 43. As a result, the cell outputted by theoriginal terminal 11 arrives at and is accepted by the terminatingterminal 13 via the path decided by call control.

Thereafter, the originating terminal 11 sends the cell to theterminating terminal 13 in successive fashion. The terminating terminal13 assembles the information field DT contained in the received cell andrestores the original data.

-   -   (d) Tag information

FIG. 5 is a diagram showing the detailed composition of the ATM cell towhich the tag TAG has been added. TAG represents one-byte taginformation, HD a first-byte header and PLD a 48-byte payload. Theheader HD contains the virtual path identifier VPI, the virtual channelidentifier VCI, the generic flow control GFC used in flow controlbetween links, a payload type PTI, the cell loss priority CLP and theheader error code HEC.

The tag includes a copy designating bit C (in which “0” indicatesone-to-one communication and “1” represents broadcast communication), aninter-switch path selection HW (a1, a2) (in case of a 4×4 ATM switch),and a reserve bit RES for when the switch is enlarged in scale.

FIG. 6 is a table for describing the relationship between the taginformation and outgoing path. The path of the entered ATM cell isdecided by the four bits C, a1, a2 and S. In FIG. 6, “x” signifies“don't care” (i.e., the bit may be “0” or “1”), and the black circlesindicate output to an outgoing path.

Further, C=1, S=0 signifies broadcast, with the ATM switch 32 outputtingthe input cell to outgoing paths of all terminals with the exception ofthe server. C=0, S=1 signifies output solely to the server, with the ATMswitch 32 outputting the input cell solely to the server. C=0, S=0signifies output of the cell to an outgoing path that conforms to thecombination of a1 and a2, with the ATM switch 32 outputting the inputcell to the prescribed outgoing path that conforms to the combination ofa1 and a2.

-   -   (e) ATM switch

FIG. 7 is a diagram showing the construction of an n×n (n=3) ATM switch.The ATM switch includes tag information detection circuits I₁˜I₃,transmission information delay circuits D₁˜D₃, demultiplexers DM₁˜DM₃,tag information decoding circuits DEC₁˜DEC₃, which construct a celldistribution unit CELD, buffer memories such as FIFO (first-in,first-out) memories FM₁₁˜FM₃₃, selectors SEL₁˜SEL₃, and arrival ordermanagement FIFOs AOM₁˜AOM₃. Each arrival order management FIFO(AOM₁˜AOM₃) is connected to the output terminals of the informationdecoding circuits DEC₁˜DEC₃ and stores the order in which cells arriveat the corresponding three buffer memories FM₁₁˜FM₁₃, FM₂₁˜FM₂₃,FM₃₁˜FM₃₃. These FIFOs control the corresponding selectors SEL₁˜SEL₃ sothat cells are read out of the three buffer memories in the order ofcell arrival and sent to outgoing lines #1˜#3.

Cells that enter input terminals #1˜#3 have the format shown in FIG. 5.Detection lines I_(i) (i=1˜3) extract the tag information TAG containedin the input signal and send the information to the decoder circuitsD_(i) (i=1˜3). If the entering tag information TAG indicates the outputterminal #j (j=1˜3), the decoder circuit DEC_(i) operates thedemultiplexer DM_(i) by a changeover signal S_(i) to send the cell tothe FIFO memory FM_(ji). For example, if the tag information TAGcontained in the cell which has entered from the input terminal #1indicates the output terminal #2, the decoder circuit DEC₁ operates thedemultiplexer DM₁ so that the information from the input terminal #1enters FM₂₁. The arrival order management FIFO (AOM_(i)) is connected tothe output terminals of the tag information decoding circuits DEC₁˜DEC₃and stores the order in which cells arrive at the corresponding threebuffer memories FM_(i1)˜FM_(i3). For example, if cells arrive in theorder of buffer memory FM₁₁→FM₁₂→FM₁₃→FM₁₂→. . . , buffer memoryidentification codes are stored in the arrival order management FIFO(AOM₁) in the order of cell arrival, i.e., in the manner 1→2→3→2→. . . .Thereafter, the arrival order management FIFO (AOM₁) controls thecorresponding selector SEL_(i) so that cells are read out of the threebuffer memories FM_(i1)˜FM_(i3) in the order of cell arrival and sent tothe outgoing line #i.

A buffer function is thus obtained by providing the FIFO memory FM_(ij)with a capacity equivalent to a plurality of cells. This makes itpossible to deal satisfactorily with a case in which there is atemporary increase in transmission data. Further, since cells are readout of the buffer memories FM_(i1)˜FM_(i3) in the order of cell arrival,equal numbers of cells reside in the buffer memories FM_(i1)˜FM_(i3).This is helpful in avoiding situations in which cells are discardedowing to overflow of the buffer memories.

In FIG. 7, an ATM switch for which n=3 holds is illustrated for the sakeof explanation. However, an ATM switch in which n=5 holds can be readilyimplemented through a similar arrangement. In such case, tag informationdecoding circuits DEC₁˜DEC₅ would perform the decoding processing shownin FIG. 6, the input cells would be stored in FIFO buffers FM_(ij)conforming to the prescribed outgoing lines (outputs 1˜5) and the cellswould be stored in the arrival order management FIFOs in the order ofarrival.

FIG. 8 is diagram showing a simplified representation of the ATM switch.Buffer memories FM₁₁˜FM_(mm) are placed at the intersections betweenm-number of input links and m-number of output links. The ATM switch ofFIG. 7 corresponds to the portion surrounded by the dashed line.

-   -   (f) Broadcast from server

In a case where an ATM address of another party's terminal requested bya certain terminal has not been registered in the ATM address table 21a,the server 21 transfers (broadcasts) an interrogation request cell forthe ATM address to all terminals via the ATM exchange 31.

FIG. 9 is a diagram for describing the broadcast method. The value ofthe VPI/VCI of the broadcast cell outputted by the server 21 is decidedon as being a fixed value (=FF−FFFF) beforehand.

The broadcast means 21c of server 21 enters an ATM cell into ATMexchange 31, the ATM cell having {circle around (1)} FF−FFFF as VPI/VCI,{circle around (2)} a protocol address of the output party's terminal asdata and {circle around (3)} data to the effect that the cell is aninterrogation for the ATM address.

In a case where VPI/VCI=FF−FFFF holds, the server accommodate section 34of the ATM exchange 31 adds tag information TAG (C=1, S=0) onto theinput cell and enters the cell into the ATM switch 32. As a result, theATM switch 32 outputs the ATM cell to the outgoing lines (outputs 1˜4)of all terminals via the buffers FM₅₁˜FM₅₄ and transfers the cell to allterminals.

In summary, the server 21 and all terminals 11˜14 are interconnectedbeforehand in the ATM exchange 31 by PVCs (permanent virtual channels)having identical values. When an interrogation request cell having theabove-mentioned PVC has entered from the server 21, a cell copy is madein the ATM exchange 31 and the interrogation request cell is transferredto all terminals 11˜14.

More specifically, when the VPI/VCI of the broadcast cell is FF−FFFF andthe cell for which VPI/VCI=FF−FFFF holds has entered from the server 21,the server accommodating section 34 adds on the tag information TAG sothat the cell will be entered into all terminals and transfers the tagto the ATM switch 32. On the basis of the tag information TAG, the ATMswitch 322 broadcasts the input cell to all terminals.

It should be noted that all terminals 11˜14 are divided up into aplurality of groups in advance, the server 21 transfers an interrogationrequest cell to all terminals of the first group and performs monitoringto determine whether a prescribed terminal has answered with the ATMaddress within a set period of time. If notification of the ATM addressis not received within the set time period, the server transfers theinterrogation request cell to all terminals of the next group. Thus, theserver transfers the interrogation request cell group by group whilesuccessively changing the group until the prescribed terminal answerswith the ATM address.

-   -   (g) Control for sending/receiving ATM-ARP message

Control for sending and receiving an ATM-ARP message (an ATM addressinterrogation message/ATM address answer message) is performed in themanner set for the below,

-   -   -   (g-1) A control connection is set beforehand through the            following steps {circle around (1)}-{circle around (3)}:

{circle around (1)} The VPI/VCI of the cell for the ATM-ARP message oneach of the terminal lines 41˜44 is made FF−FFFF. More specifically, theVPI/VCIs of the ATM address interrogation cells sent from the terminals11˜14 to the server 21 are FF−FFFF.

{circle around (2)} VPI/VCIs are assigned to terminals in regular orderon the server side. That is, the VPI/VCIs of the cells for the ATM-ARPmessages sent from the server to the terminals 11˜14 are made asfollows, respectively:00-0001, 00-0002, 00-0003, 00-0004.

{circle around (3)} In order to broadcast the ATM address interrogationcell to all terminals, the VPI/VCI of the cell is made FF−FFFF on theserver side. This is in addition to {circle around (2)} above.

FIG. 10 is an explanatory view showing connections between the server 21and terminals 11˜14 in a case where control connections are set in themanner described above.

-   -   -   (g-2) General features of communication method

When cells (ATM address interrogation cells) for which VPI/VCI=FF−FFFFholds enter from the terminals 11˜14, the terminal accommodatingsections 33a˜33d replace the VPI/VCIs with 00-0001˜00-0004, add the taginformation TAG (C=0, S=1), onto the cells and then transfer the cellsto the ATM switch 32.

On the basis of the tag information TAG (C=0, S=1), the ATM switch 32transfers the input cells (ATM address interrogation cells) to theserver 21.

If an ATM address interrogation cell is received, the server 21 obtainsthe ATM address and notifies the terminal that issued the interrogationcell. It should be noted that the server 21 can identify from whichterminal a cell has arrived depending upon the VPI/VCI (=00-0001,˜00-0004) updated by the terminal accommodation sections 33a˜33d.

The answer cells of the ATM addresses from the server 21 to theterminals 11˜14 have VPI/VCIs (=00-0001˜00-0004) conforming to theterminals which are the destination of transmission. When the answercell enters, the server accommodation section 34 updates the value ofthe VPI/VCI from 00-0001˜00-0004 to FF−FFFF, adds on the tag informationTAG (S=0, C=0, a1, a2=destination terminals) and transfers the cell tothe ATM switch 32. On the basis of the tag information TAG, the ATMswitch 32 switches the input cell, sends the cell to the line to whichthe prescribed terminal is connected and enters the cell into thisterminal.

In the case of a broadcast, on the other hand, the interrogation requestcell sent from the server 21 has FF−FFFF as the VPI/VCI. When theinterrogation cell for which VPI/VCI=FF−FFFF holds enters, the serveraccommodating section 34 adds on the tag information TAG (C=1, S=0)specifying all paths and then transfers the cell to the ATM switch 32.In this case, the value of the VPI/VCI is not changed. On the basis ofthe tag information TAG (C=1, S=0), the ATM switch 32 switches to allpaths and enters the cell into all terminals.

-   -   (h) Communication sequence of the invention

A broadcast method of broadcasting an interrogation request to allterminal:

FIG. 23 is a diagram for describing the broadcast method. Terminals 1a,1b, 1c are connected to an ATM-LAN 2. According to the broadcast method,the ATM address is interrogation request is broadcast within the networkif the ATM address of the other party's terminal is unknown at themoment a communication request is generated, and a prescribed terminalresponds to this interrogation by answering with its own ATM address.For example, if the ATM address of terminal 1b is unknown to theterminal 1a when this terminal communicates with the terminal 1b in FIG.23, the terminal 1a broadcasts an ATM address interrogation request cell(which has the protocol address of terminal 1b) within the network. Theterminal 1b, which is that terminal having a protocol address identicalwith that contained in the received cell, answers the terminal 1a withits own ATM address. The terminal 1a uses the received ATM address tocall the terminal 1b and communicate with it.

If the ATM address of another party's terminal is unknown at the momenta communication request is issued in the broadcast method, a broadcastis made within the network and the terminal is interrogated directly.Unlike the server method, implementation is easy because it isunnecessary to create a data base in advance. However, in cases wherefrequent communication is made with an unspecified terminal whose ATMaddress is unknown, broadcast of the interrogation request is madewhenever a communication request is issued. A problem which arises as aconsequence is an increase in control traffic. This problem becomesparticularly pronounced with an increase in the number of terminals ordepending upon the scale of the network.

FIG. 11 is a diagram for describing the communication sequence of thepresent invention.

{circle around (1)} The originating terminal 11 refers to its own cachememory and determines whether the ATM address of the other party hasbeen registered. It should be noted that information regarding a partyto be communicated with will not have been registered in the cachememory when power is introduced to the system. If the information hasbeen registered, set-up is executed to set a path using this ATM addressand communication is carried out. If the information has not beenregistered, however, the originating terminal 11 puts an ATM-ARP request(an ATM address interrogation request) message into the form of a celland sends the cell to the server 21 in order to inquire as to the ASTMaddress of the communicating party 14. FIG. 12 illustrates the format ofthe ATM-ARP request message/answer message.

The message includes protocol type 100, which indicates the type (IP,etc.) of host protocol; ATM address length 101, which indicates addresslength of the ATM address used in an ATM network; protocol addresslength 102, which indicates address length (four bytes in case ofprotocol type IP) of the host protocol; an operation code (“1”: request,“2”: answer) 103; ATM address (source address) 104 of the requestingterminal; a protocol address (source address) 105 of the requestingterminal; ATM address 106 of the target terminal, which is all “1's” orall “0's” in case of a request message; with the ATM address beinginserted in case of the answer message; and protocol address 107 of thetarget terminal.

{circle around (2)} Upon receiving the ATM-ARP request from the terminal11, the server 21 determines whether the ATM address corresponding tothe protocol address of the target terminal contained in the request hasbeen registered in the ATM address table 21a. If the ATM address hasbeen registered, an ATM-ARP answer message containing this information(ATM address) is formed into a cell and sent back to the terminal 11.

If the ATM address has not bene registered, the server 21 transfers theATM-ARP request to all terminals using the broadcast function of the ATMswitch 32.

{circle around (3)} Upon receiving the ATM-ARP request transferred(broadcast) from the server 21, each of the terminals 11˜14 determineswhether the protocol address of the target terminal contained in thisrequest agrees with its own protocol address. If agreement is achieved,the terminal forms the ATM-ARP answer message indicating its own ATMaddress into a cell and sends the message back to the server 21.

{circle around (4)} Upon receiving the ATM-ARP message from the terminal14, the server 21 obtains the ATM address of the target terminal 14. Thesearch/registration means 21b correlates the ATM address d and thereference time with the protocol address D of the target terminal 14 andregisters the correlation in the ATM address table 21a, as shown in FIG.3. If the ATM address table 21a is saturated (full), the entry havingthe oldest reference time is deleted and the a new entry is registered.It should be noted that an arrangement can be adopted in which, ratherthan storing the reference time, correlation are stored in orderstarting from the oldest correlations by the LRU (least recently used)method.

{circle around (5)} Further, when the ATM-ARP answer message is receivedfrom the terminal 14, the server 21 transfers the ATM address containedin the answer message to the requesting terminal 11 that transmitted theATM-ARP request message.

{circle around (6)} Upon receiving the ATM-ARP answer message at {circlearound (2)} or {circle around (5)}, the terminal 11 that issued theATM-ARP request message at {circle around (1)} above recognizes the ATMaddress of the communicating party 14, correlates this ATM address withthe protocol address and saves the correlation in its own cache memory.

{circle around (7)} Further, the terminal 11 executes set-up using theATM address of the communicating party, establishes a path andcommunicates with the terminal 14.

Thus, in a case where the ATM address has been registered in the ATMaddress table 21a, the server 21 operates in the same manner as in theconventional server method. If the ATM address has not been registeredin the ATM address table 21a, however, the server 21 can obtain thetarget ATM address by broadcast of the ATM-ARP request message.Accordingly, the server need not register the information of allterminals in the ATM address table 21a in advance, and the storedcontent of the ATM address table can be perfected by a learningfunction. This is effective in terms of implementing the ATM addresstable by small-scale circuitry.

FIG. 13 is a diagram for describing another communication sequence ofthe present invention. This is for a case in which an ATM address forwhich an inquiry has been made by the ATM-ARP request from a certainterminal has been registered in the ATM address table 21a. Specifically,this is an example of a case in which the terminal 12 communicates withthe terminal 14 after the communication sequence of FIG. 11.

{circle around (1)} The terminal 12 that has issued the communicationrequest refers to its own cache memory and determines whether the ATMaddress of the communicating party has been registered. If the ATMaddress has not been registered, set-up is executed to set a path usingthis ATM address and communication is carried out. If the informationhas not been registered, however, the terminal 12 puts the ATM-ARPrequest message into the form of a cell and sends the message to theserver 21 in order to inquire as to the ATM address corresponding to theprotocol address of the communicating party 14.

{circle around (2)} Upon receiving the ATM-ARP request from the terminal12, the server 21 determines whether the ATM address corresponding tothe protocol address of the terminal 14 contained in the request hasbeen registered in the ATM address table 21a. If the ATM address hasbeen registered, an ATM-ARP answer message containing this information(ATM address) is formed into a cell and is sent back to the terminal 12.

{circle around (3)} Upon receiving the ATM-ARP request from the server21, the terminal 12 recognizes the ATM address of the communicatingparty 14, correlates this ATM address with the protocol address andsaves the correlation in its own cache memory.

{circle around (4)} Next, the terminal 12 executes set-up using the ATMaddress of the communicating party, establishes a path and communicateswith the terminal 14.

Thus, in a case where the ATM address has been registered in the ATMaddress table 21a, the server 21 operates in the same manner as in theconventional server method.

-   -   (i) Processing at each part of communication sequence        -   (i-1) Processing by originating terminal FIG. 14 is a            flowchart of processing executed by an originating terminal            when a communication request is issued.

When a communication request is issued (step 201), the terminal refersto its own cache memory and determines whether the ATM address of thecommunicating terminal is en entry in the memory (step 202). If ATMaddress is an entry, the terminal executes set-up using the ATM address,establishes a path and performs communication (step 203),

If the ATM address is not an entry in the cache memory, however, theterminal puts the ATM-ARP request message into the form of a cell andsend the message to the server 21 in order to inquire as to the ATMaddress corresponding to the protocol address of the communicating party(step 204).

The terminal then waits for transmission of the ATM-ARP answer messagefrom the server 21 (step 205). If the ATM-ARP answer message isreceived, then the terminal registers the ATM address of the otherparty's terminal contained in the message in the cache memory (step 206)and subsequently executes set-up using this ATM address, establishes apath and performs communication step (step 203).

-   -   -   (i-2) Processing by terminating terminal

FIG. 15 is a flowchart of processing executed by each terminal when theserver broadcasts the ATM-ARP request message to all terminals.

Upon receiving the ATM-ARP request message (an ATM address interrogationrequest message) from the server 21 (step 301), each terminal determineswhether the protocol address of the target terminal contained in thisrequest agrees with its own protocol address (step 302). If agreementwith its own protocol address is not achieved, the terminal endsprocessing. If agreement is achieved, the terminal creates an ATM-ARPresponse message in order to give notice of its own ATM address andsends the message back to the server 21 in the form of a cell (step303).

-   -   -   (i-3) Processing flow of server

FIG. 16 is a flowchart of processing executed by the server forreceiving an ATM-ARP request.

Upon receiving an ATM-ARP request from a prescribed terminal (step 400),the server 21 registers the corresponding relationship between theprotocol address and ATM address of the original terminal contained inthe request, as well as the time, in the ATM address table 21a (step401).

Next, the server 21 determines whether the ATM address corresponding tothe protocol address of the target terminal has been registered in theATM address table 21a (step 402). If the ATM address has beenregistered, the reference time in the ATM address table 21a is updated(step 403). The server 21 thenceforth creates an ATM-ARP responsemessage in order to give notice of the above-mentioned ATM addressand'sends the message back to the requesting terminal in the form of acell (step 400).

On the other hand, if it is found at step 402 that the desired ATMaddress has not bee registered, the server 21 transfers the ATM-ARPrequest to all terminals using the broadcast function of the ATM switch42 (step 405). Next, the server waits for reception of the ATM-ARPanswer message in response to the above-mentioned ATM-ARP request (step406).

If the ATM-ARP answer message is received from a prescribed terminal,the server 21 newly registers the ATM address contained in this messageas well as the reference time in the ATM address table 21a (step 407).

Processing for registering the ATM address anew is as follows: Theserver 21 checks to see whether the ATM address table 21a is full (step407a). If the table is not full, the server 21 refers to the ATM addressusing the protocol address as index, and newly registers the ATM addressand reference time in the ATM address table 21a in correspondence withthe protocol address of the terminal (step 407b). In a case where theATM address table 21a is full, the server deletes the entry having theoldest reference time to form a vacancy (step 407c) and registers thenew entry (the ATM address and reference time) in this vacancy (step407b).

After making the new registration, the server 21 creates an ATM-ARPanswer message to notify of the ATM address and sends the message backto the requesting terminal in the form of a cell (step 404).

The foregoing is for a case in which the ATM-ARP request is broadcast toall terminals en masse at step 405. However, all of the terminals 11˜14can be divided up into a plurality of groups and the request can bebroadcast group by group.

FIG. 17 is a flowchart of such “multicasting”.

If it is found at step 402 in FIG. 16 that the desired ATM address hasnot been registered, the server 21 performs the operation 1→i (step405a) and then transfers the ATM-ARP request to all terminals of an ithgroup using a multicasting function of the ATM switch 32 (step 405b).Next, the server 21 determines whether the ATM-ARP answer message whichis a response to the above-mentioned ATM-ARP request has beentransmitted from the prescribed terminal (step 405c). If the answermessage has not been transmitted, the server determines whether timethat has elapsed from the multicast has surpassed a set time (step405d). If the decision rendered is NO, then the program jumps to step405c and the server wishes for reception of the ATM-ARP answer message.

If the ATM-ARP answer message is not received even upon elapse of theset time, the group is incremented by the operation i+1→i (step 405e)and processing from step 405b onward is executed with regard to the nextstep.

If the ATM-ARP answer message is received from the prescribed terminalwithin the set time, then the program jumps to step 407 of FIG. 16 andexecutes the processing from this step onward.

It should be noted that the ATM address table 21a holds N-number ofcorresponding relationships between protocol addresses and ATM addressesreferred to most recently. Accordingly, by arranging is so that aterminal periodically sends an ATM address interrogation request for itsown terminal to the server 21, the corresponding relationship betweenthe terminal's own protocol address and the ATM address can be kept inthe ATM address table at all times.

-   -   (j) Construction of server

FIG. 18 is a block diagram showing the construction of the server 21.The server 21 includes the ATM address table 21a, a cell receiver 51, amessage receiver 52, a reception buffer 53, a CPU 54, a main memory 55,a working memory 56, a transmission buffer 57, a message transmitter 58and a cell transmitter 59.

The operation of each unit in response to an ATM-ARP request will now bedescribed.

Upon receiving a cell form the ATM exchange 31, the cell receiver 51assemblies a cell for every VPI/VCI and transfers the cell to themessage receiver 52. The latter transfers the message received from thecell receiver 51 to the reception buffer 53 and notifies the CPU 54, bymeans of an interrupt, of the fact that an ATM address interrogationrequest message or answer message has been received.

When the interrupt to notify of reception is generated, the CPU 54 readsin the message from the reception buffer 53, analyzes the operation code(see FIG. 12) contained in the message and identifies whether themessage is in the ATM address interrogation request message or answermessage.

When received message is interrogation request message

If the received message is the interrogation request message, the CPU 54registers, in the table 21a, the corresponding relationship between theprotocol address and ATM address of the originating terminal containedin the message. Next, the CPU 54 executes processing to search the ATMaddress table 21a using the protocol address of the target as an index.If the target ATM address has been registered in the ATM address table21a, the CPU 54 creates an answer message for giving notice of the ATMaddress, writes the message in the transmission buffer 57 and requeststhe message transmitter 58 to transfer the answer message to theoriginating terminal based upon the prescribed VPI/VCI.

If the target ATM address has not been registered in the ATM addresstable 21a, however, the CPU 54 transfers the interrogation requestmessage stored in the reception buffer 53 to the transmission buffer 57and requests the message transmitter 58 to carry out a transfer basedupon the VPI/VCI for the purpose of broadcast.

When received message is answer message

If the received message is the answer message, on the other hand, theCPU 54 correlates the target ATM address contained in the answer messagewith the target protocol address, registers the correlation in the ATMaddress 21a and transfers the answer message in the reception buffer 53to the transmission buffer 57 as is. Thereafter, the CPU 54 requests themessage transmitter 58 to transfer the above-mentioned answer message tothe originating terminal based upon the prescribed VPI/VCI.

Upon receiving the transmission request from the CPU 54, the messagetransmitter 58 transfers the data in the transmission buffer 57 to thecell transmitter 59 and gives notice of the value of the VPI/VCI. Thecell transmitter 59 transfers the message, which has been received fromthe message transmitter 58, to the ATM exchange 31 upon forming themessage into a cell based upon the VPI/VCI of which it has beennotified.

-   -   (k) Construction of terminal

FIG. 19 is a diagram showing the construction of the terminals 11˜14.Numeral 60 denotes the main body of a work station (WS) or personalcomputer (PC), which has an ATM interface card 61. The ATM interfacecard 61 includes a system-bus interface circuit 62, a local processor63, a local memory 64, a buffer memory 65, a CLAD (cellassembly/disassembly) circuit 66 and a physical interface circuit 67.

The operation of each component of the ATM interface card will now bedescribed.

The ATM interface card 61 mounts the local processor 63 and the localmemory 64, which stores various programs, and is connected with the WSor PC 60 by loose coupling implemented by communication betweenmemories. Examples of the programs are a program for managing theoverall ATM interface card, a control program for the ATM addressnotification request and for giving notice of an answer, a communicationcontrol program, etc.

The system-bus interface circuit 62 has a control mechanism forcommunicating with the WS or PC 60. The circuit 62 provides an interfacedependent upon the WS or PC. A communication request message generatedby an application in the WS is transferred to the local memory 64 viathe system-bus interface circuit 62.

Upon receiving the communication request message, the local processor 63obtains the ATM address of the other party's terminal based upon thedestination protocol address contained in the message. That is, sincethe correspondence between the protocol address and the ATM address hasbeen stored in, say, a storage area (address cache memory) in the localmemory 64, the processor 63 searches the address cache memory.

If the ATM address corresponding to the destination protocol address hasnot been registered in the cache memory, the local processor 63 createsthe ATM address interrogation request message, stores the message in thebuffer memory 65 and starts up the CLAD circuit 66. As a result, theCLAD circuit 66 forms the ATM address interrogation request message intoa cell (VPI/VCI=FF−FFFF) and transfer the cell to the ATM exchange 31via the physical interface circuit 67.

When notice of the ATM address in response to the interrogation requestis received from the ATM exchange 31, the local processor 63 registersthe ATM address in the address cache memory. Thereafter, the localprocessor 63 starts up the communication control program, creates aset-up message using the received ATM address under the control of thecommunication program and stores the message in the buffer memory 65.The CLAD circuit 66 forms the set-up message into a cell and transfersthe cell to the ATM exchange 31 via the physical interface circuit 67.It should be noted that if the ATM address has been registered in theaddress cache memory, the local processor 63 creates the set-up messageimmediately without making an inquiry and transfers the message to theATM exchange 31.

The ATM exchange 31 executes call processing in response to the set-upmessage and sends back a connect message. Upon receiving the connectmessage via the physical interface circuit 67, the CLAD circuit 66 formsthe message into a cell, stores the cell in the buffer memory 65 andnotifies the local processor 63 of receipt of the message. As a result,the local processor 63 accepts the connect message from the buffermemory 65, verifies establishment of the communication path based uponthe message and terminates the communication control program.

Thereafter, the local processor 63 starts message transfer using theidentifier (VPI/VCI) of the communication path of which it has beennotified by the connect message. More specifically, in response toestablishment of the communication path, the local processor 63 storesthe message received from the WS or PC in the buffer memory 65 andnotifies the CLAD circuit 66 of the identifier (VPI/VCI) of the setcommunication path. As a result, the CLAD circuit 66 forms the messagein the buffer memory 65 into a cell using the value of the VPI/VCI andtransfers the cell to the ATM exchange 31 via the physical interfacecircuit 67.

In a case where a cell stream is received from the ATM exchange 31 viathe physical interface circuit 67, the CLAD circuit 66 disassembles thecell and assembles a message, stores the message in the buffer memory 65and then notifies the local processor 63 of the fact that the messagehas been received. In response to notification of receipt from the CLADcircuit 66, the local processor 63 accepts the message from the buffermemory 65 and transfers the message to the WS via the system-businterface circuit 62.

-   -   (l) Construction of server accommodation section

FIG. 20 is a block diagram showing the construction of a serveraccommodating section 34. The construction is the same for the terminalaccommodating sections 33a˜33d as well. The server accommodating section34 includes a physical interface 71 for sending cells to and receivingcells from the server, a traffic monitoring circuit 72 for determiningwhether cells are being transmitted at a declared speed, a header tagtable (routing table) 73 which stores {circle around (1)} taginformation and {circle around (2)} a new VPI/VCI, which is to bereplaced, in correspondence with a VCI, a header replacing circuit 74, aswitching interface circuit 75 for administering interfacing with theATM exchange 31, a cell buffer 76 which stores a cell entered from theATM exchange 31, and a traffic shaper 77 which performs control in sucha manner that cells are transmitted at a desired traffic.

In accordance with the present invention, the arrangement is such thatif an ATM address has been registered in the ATM address table of aserver when an interrogation request has been issued for this ATMaddress, the target ATM address can be obtained through an operationsimilar to that performed in the conventional server method. If the ATMaddress has not been registered in the ATM address table, however, thetarget ATM address can be obtained by broadcasting the interrogationrequest for the ATM address. In other words, according to the invention,ATM addresses are managed by making joint use of the server method andbroadcast method. This makes it possible to hold down at increase incontrol traffic. Moreover, ATM addresses can be perfected bysuccessively registering corresponding relationships, which have beenfound using the broadcast method, in the ATM address table. In addition,it is possible to dispense with a task for initially setting the ATMaddress table and a task for updating the table when terminals are addedon or moved.

Further, in accordance with the present invention, all terminals aredivided up into a plurality of groups. When a broadcast is made, theserver transfers the ATM address interrogation request cell to allterminals of the first group. If there is no notice of answer of the ATMaddress within a set time, the server transfers the interrogationrequest cell to all terminals of the next group. Thenceforth, and insimilar fashion, the server transfers the interrogation request cellwhile successively changing groups until the prescribed terminal answerswith the ATM address. As a result, there is a good possibility that thedesired ATM address will be obtained without broadcasting theinterrogation request cell to all terminals. Consequently, an increasein traffic can be suppressed.

Furthermore, in accordance with the invention, (1) upon receivingnotification of the ATM address from the prescribed terminal, the servernewly registers the correspondence between the protocol address of thisterminal and the ATM address, of which it has been notified, in the ATMaddress table. Further, (2) the server registers, in the ATM addresstable, the corresponding relationship between the protocol address ofthe originating terminal, which address is contained in the ATM addressinterrogation request received from the originating terminal, and theATM address. Accordingly, if an inquiry for the above-mentioned ATMaddress is issued after registration, it is unnecessary to broadcastthis interrogation request; the ATM address can be obtained in simplefashion from the ATM address table.

Further, in accordance with the present invention, if the ATM addresstable is full when the prescribed terminal has answered with the ATMaddress, the server erases the oldest corresponding relationshipreferred to and newly registers the ATM address of which it has beennotified in the ATM address table. As a result, a large-capacity ATMaddress table is unnecessary and the scale of the server hardware can beminimized.

Furthermore, in accordance with the invention, a terminal periodicallysends an ATM address interrogation request for its own terminal to theserver, whereby the corresponding relationship between the terminal'sown protocol address and the ATM address can be kept in the ATM addresstable at all times.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

1. An address management method in a communication system equipped witha plurality of terminals, and a server having an address table forstoring registering a corresponding relationship between a protocolfirst address and terminal a second address of each terminal, and anexchange which accommodates each terminal and the server, said themethod comprising the steps of: a first step in which an originatingterminal sends a terminal address interrogation request to the server ifthe terminal address of another party's terminal is unknown at the timeof communication; a second step in which the server, upon receiving theterminal address interrogation request from the terminal, refers to theaddress table and searches for a terminal address corresponding to aprotocol address contained in said interrogation request; a third stepin which, if a terminal address corresponding to said protocol addressis obtained from the address table, the server notifies the terminal ofthis terminal address; a fourth step in which, if the terminal addressis not obtained from the address table, the server transfers theterminal address interrogation request containing said protocol addressto all terminals via the exchange; sending, to the server by anoriginating terminal, an address interrogation request which includes afist value indicative of a request and a first address; transferring, toa plurality of terminals by the server, the address interrogationrequest which includes the first value and the first address; the fifthstep in which, whenreceiving, by each terminal receives the terminaladdress interrogation request transferred from the server, the terminaldetermines; determining by each terminal whether the protocol firstaddress contained included in the address interrogation request receivedfrom the server agrees with its a terminal's own protocol first addressand notifies the server of its own terminal address if agreement isachieved; and, ; a sixth step in which the server notifies theoriginating terminal of the terminal address of which it has beennotified notifying, by each terminal, in response to the addressinterrogation request, the server of an answer which includes aterminal's own second address which is not registered in the server anda second value indicative of an answer when agreement is achieved;receiving, from one of the plurality of terminals by the server, theanswer which includes the second value and the second address whichcorresponds to the first address; and registering, in the server, acorresponding relationship between the first address and the secondaddress which is included in the answer.
 2. The method according toclaim 1, in the communication system which includes a switch or exchangewhich accommodates each terminal and the server, wherein said fourth thetransferring step includes: a step in which the exchange or switchconnects the server with all a plurality of terminals by PVCs (permanentvirtual channels) having identical values ; and a step in which, when aterminal an address interrogation request having said identical apredetermined value for a PVC has entered from the server, the exchangeor switch performs cell copying, whereby said the address interrogationrequest cell is transferred to all the plurality of terminals.
 3. Themethod according to claim 1, in the communication system which includesa switch or exchange which accommodates each terminal and the server,wherein said fourth the transferring step includes: a step in which theexchange or switch connects the server with all a plurality of terminalsby PVCs (permanent virtual channels) having identical values and dividesall the plurality of terminals into a plurality of groups; a step inwhich, when a terminal an address interrogation request having saididentical a predetermined value for a PVC has entered from the server,the exchange or switch performs cell copying, wherein said the addressinterrogation request cell is transferred to all terminals in firstgroup; a step in which the server performs monitoring to determinewhether a prescribed terminal has answered with a terminal secondaddress within a set period of time; a step in which the server sendsthe address interrogation request cell to all the plurality of terminalsof the next group if no terminal answers with a terminal second addresswithin the set period of time; and a step in which the server transfersthe address interrogation request cell while successively changing thegroup until a prescribed terminal answers with a terminal secondaddress.
 4. The method according to claim 1, further comprising aseventh step in which, when the server receives the answer of theterminal address from the terminal, the server newly stores thecorresponding relationship between said protocol address and theterminal address, of which it has been notified, in the address table.5. The method according to claim 1, further comprising an eighth step inwhich the server stores, in the address table, correspondingrelationship between the protocol address of the originating terminaland the terminal address which are contained in the terminal addressinterrogation request received from said originating terminal.
 6. Themethod according to claim 1, further comprising: a seventh step inwhich, when the server receives the answer of the terminal address fromthe terminal, the server deletes a corresponding relationship, referredto least recently, between a protocol address and terminal address ifthe address memory is full An address management method in acommunication system equipped with a plurality of terminals, and aserver for registering a corresponding relationship between a firstaddress and a second address of each terminal, the method comprising thesteps of: sending, to the server by an originating terminal, an addressinterrogation request which includes a first value indicative of arequest and a first address; transferring, to a plurality of terminalsby the server, the address interrogation request which includes thefirst value and first address; receiving, by each terminal, the addressinterrogation request transferred from the server; determining by eachterminal whether the first address included in the address interrogationrequest from the server agrees with a terminal's own first address;notifying, by the terminal, in response to the address interrogationrequest, the server of an answer which includes a terminal's own secondaddress which is not registered in the server and a second valueindicative of an answer when agreement is achieved; receiving, from oneof the plurality of terminals by the server, the answer which includesthe second value and the second address which corresponds to the firstaddress; deleting a corresponding relationship, referred to leastrecently, between a first address and a second address if the servercannot accommodate a corresponding relationship between the firstaddress and second address included in the answer received form aprescribed terminal; and an eight stepregistering, in whicha memory bythe server newly stores the, a corresponding relationship between saidprotocolthe first address and the terminalsecond address, of which ishas been notified,is included in the address tableanswer.
 7. The methodaccording to claim 1, further comprising a ninth step in which eachterminal sends periodically the server an interrogation request for itsown terminal's address, whereby the corresponding relationship betweenits own terminal's protocol address and the terminal address is kept inthe address table.
 8. A communication system equipped with a pluralityof terminals, and a server having an address table for storingregistering a corresponding relationship between a protocol firstaddress and terminal second address of each terminal, and an exchangewhich accommodates each terminal and the server, wherein each of thesaid the terminals comprises: means for sending a terminal , to theserver, an address interrogation request to the server if the terminaladdress of another party's terminal is unknown at the time ofcommunication which includes a first value indicative of a request and afirst address; and communication means for communicating with the otherparty's terminal via the exchange using a terminal address of which ithas been notified by the server in response to the interrogationrequest; and Terminal address answering means for answering the serverwith an answer including its own terminal address ifwhich is notregistered in the server and a second value indicative of an answer whena protocolfirst address contained, included in an a terminal addressinterrogation request transferredwhich has been received from the serveragrees with its own protocolfirst address; and saidthe server comprises:means for referring to the address table and searching for a terminaladdress corresponding to a protocol address contained in a terminaladdress interrogation request from a terminal; means which, if aterminal address corresponding to said protocol address has not beenregistered in the address table, is for transferring the terminaladdress interrogation request containing said protocol which includesthe first value and the first address to all a plurality of terminalsvia the exchange ; and means for notifying the terminal which has issuedthe interrogation request of a terminal address found from the addresstable or of a terminal address obtained by an answer from a terminalregistration means for registering, in the server, a correspondingrelationship between the first address and the second address which isincluded in the answer which has been received from one of the pluralityof terminals in response to the address interrogation request which hasbeen transferred from the server.
 9. The communication system accordingto claim 8, wherein said exchange comprises: means for connecting theserver with all terminals by PVSs (permanent virtual channels) havingidentical values; and means which, when a terminal address interrogationrequest having said identical value for PVC has entered from the server,is for performing cell copying and transferring said interrogationrequest cell to all terminals.
 10. The communication system according toclaim 8, wherein said server has registration means which, when theserver receives the answer of the terminal address from a prescribedterminal, is for newly storing the corresponding relationship between aprotocol address and the terminal address, of which it has beennotified, in the address table.
 11. The communication system accordingto claim 10 8, wherein when the server receives the answer of theterminal address cannot register a corresponding relationship betweenthe first address, and second address included in the answer which isreceived from the prescribed terminal, said the registration meansdeletes a corresponding relationship, referred to least recently,between a protocol first address and terminal second address if theaddress memory is full .
 12. A server in a communication system equippedwith a plurality of terminals, the server for managing a correspondingrelationship between a protocol address and terminal address of eachterminal, and an exchange which accommodates each terminal and theserver, said the server comprising: an address table for storing thecorresponding relationship between a protocol address and terminaladdress of each of the plurality of terminals; search means forreferring to said address table and searching for a terminal addresscorresponding to a protocol address contained in a terminal addressinterrogation request from a terminal; and interrogation means which, ifa terminal address corresponding to the protocol address has not beenregistered in the address table, is for interrogating all receiving,from an originating terminal, an address interrogation request includinga first value indicative of a request and a first address, and fortransferring the address interrogation request to a plurality ofterminals, via an exchange, or the terminal address corresponding tothis protocol address; wherein in response to receipt of a terminaladdress interrogation request from an originating terminal, said searchmeans refers to said address table to obtain the terminal addressconforming to the protocol address contained in this terminal addressinterrogation request and, if this terminal address has not beenregistered, said interrogation means interrogates the terminals forterminal address ; means for receiving, form one of the plurality ofterminals having it's own second address which is not registered in theserver, an answer including a second value indicative of an answer and asecond address which corresponds to the first address, in response tothe address interrogation request which has been transferred from theserver; and registration means for registering, in a memory, acorresponding relationship between the first address and the secondaddress which is included in the answer.
 13. The server according toclaim 12, further comprising: means for receiving notification of ananswer from a prescribed terminal in response to the terminal addressinterrogation request; and registration means for newly registering thecorresponding relationship between the protocol address and the terminaladdress, of which it has been notified, in said address table.
 14. Theserver according to claim 13 12, wherein when the server receives the ananswer of the terminal including a second value indicative of an answerand a second address from the prescribed terminal one of the pluralityof terminals, said the registration means deletes a correspondingrelationship, referred to least recently, if said address memory is fullthe server can not accommodate a corresponding relationship between thefirst address and second address, and registers, in a memory of theserver, the corresponding relationship between the protocol firstaddress and the terminal second address, of which it has been notified,in said address table which is included in the answer.
 15. The serveraccording to claim 12, wherein said terminal address the interrogationmeans divides all a plurality of terminals into a plurality of groups,interrogates all terminals of a first group for a terminal secondaddress and, if notification of an answer of a terminal including thesecond address is not received within a set period of time, interrogatesall terminals of the next group for a terminal second address.
 16. In anetwork system having a server, the method of registering in the servera corresponding relationship between a first identifier and a secondidentifier for a communication party, comprising the steps of: receivingan interrogation request including a first value indicative of a requestand a first identifier; determining a corresponding second identifier isnot registered in the server; transferring the interrogation request toa plurality of terminals which can accommodate the communication party;receiving, from a terminal having it's own second identifier which isnot registered in the server, an answer including a second valueindicative of an answer and a second identifier which corresponds to thecommunication party identified by the first identifier, in response tothe interrogation request; and registering a corresponding relationshipbetween the first identifier and the second identifier which is includedin the answer.
 17. The method according to claim 16, wherein thecorresponding relationship between the first identifier and the secondidentifier is registered in a vacancy which has been formed by deletingan entry which has a corresponding relationship between a firstidentifier and a second identifier.
 18. The method according to claim17, wherein the vacancy is formed by deleting an entry which has theoldest reference time.
 19. The method according to claim 16, wherein thesystem includes a switch or exchange and wherein the transferring stepincludes: a step in which the switch or exchange connects the serverwith a plurality of terminals by PVCs (permanent virtual channels); astep in which, when the interrogation request, in the form of a cellhaving a predetermined virtual channel identifier, is entered from theserver, the switch or exchange appends tag information indicating aterminal group to the cell, performs cell copying based on the taginformation indicating the terminal group, and transfers the cell toterminals of the terminal group.
 20. The method according to claim 16,wherein the system includes a switch or exchange and wherein thetransferring step includes: a step in which the switch or exchangeconnects the server with a plurality of terminals by PVCs (permanentvirtual channels) and divides the plurality of terminals into aplurality of groups; a step in which, when the interrogation request inthe form of a cell is entered from the server, the switch or exchangeperforms cell copying, whereby the interrogation request cell istransferred in a first group; a step in which the server performsmonitoring to determine whether a prescribed terminal has answered withits own identifier within a set period of time; a step in which theserver sends the interrogation request cell to all terminals of the nextgroup when no terminal answers with its own identifier within the setperiod of time; and a step in which the server transfers theinterrogation request while successively changing the group until aprescribed terminal answers with its own identifier.
 21. The methodaccording to claim 16, further comprising a step in which, when theserver receives the answer including the second identifier and thesecond value from the one of the plurality of terminals, the serverregisters the corresponding relationship between the first identifierand the second identifier in place of a memory in the server designatedby an index value which is calculated based on a value of the firstidentifier or the second identifier.
 22. The method according to claim16, further comprising a step in which the server periodically receivesan interrogation request including a second identifier and a secondvalue indicative of an answer from each terminal of the plurality ofterminals, whereby the corresponding relationship between the firstidentifier of its own terminal and the second identifier is kept in aserver.
 23. The method of claim 16 wherein the plurality of terminalsare a plurality of ATM terminals.
 24. The method of claim 16 wherein thefirst identifier is a protocol address.
 25. The method of claim 16wherein the second identifier is a terminal address.
 26. In a networksystem having a server, the method comprising the steps of: receiving,from an originating terminal by the server, an address interrogationrequest including a first address and a first value indicative of arequest; transferring, by the server, the address interrogation requestto a plurality of terminals; receiving, from an originating terminal bythe server, an answer including a second value indicative of an answerand second address which corresponds to a first address; deleting, fromthe server, an entry which has a corresponding relationship between afirst address and a second address from the server to form a vacancywhen the server cannot register a corresponding relationship between thefirst address and the second address which is included in the answer;and registering in a vacancy of the server a corresponding relationshipbetween the first address and the second address which is included inthe answer.
 27. The method according to claim 26, wherein the vacancy isformed by deleting the entry which has the oldest reference time.
 28. Anaddress resolution system equipped with a plurality of terminals, aswitch or exchange which accommodates each terminal of a plurality ofterminals and a server, wherein each terminal of the plurality ofterminals comprises: means for sending a terminal address interrogationrequest which includes a first value indicative of a request and a firstaddress to the server if a second address of another party's terminal isunknown at the time of communication; and means for answering the serverwith an answer including a terminal own second address and a secondvalue indicative of an answer when a first address included in aterminal address interrogation request received from the server agreeswith a terminal own first address; and the server comprises: means fortransferring the terminal address interrogation request including thefirst value indicative of the request and the first address to theplurality of terminals; and receiving means for receiving, in responseto the terminal address interrogation request which has been transferredby the server, an answer including a second address corresponding to thefirst address from one of the plurality of terminals; means forregistering in the server a corresponding relationship between the firstaddress and the second address which has been included in the answer.29. The address resolution system according to claim 28, wherein theswitch or exchange comprises: means for connecting the server with aplurality of terminals by PVCs (permanent virtual channels); and meanswhich, when a terminal address interrogation request cell having apredetermined value for a PVC is entered from the server, is forperforming cell copying and transferring of the interrogation requestcell to the plurality of terminals.
 30. The address resolution systemaccording to claim 28, wherein the server has registration means whichwhen the server receives the answer including the second addresscorresponding to the first address from one of the plurality ofterminals, is for registering a corresponding relationship between thefirst address and the second address in a place designated by an indexvalue which is calculated based on a value of the first address or thesecond address.
 31. The address resolution system according to claim 28,wherein when the server receives the answer including the second addresscorresponding to the first address from the one of the plurality ofterminals, the registration means deletes an entry which has acorresponding relationship between a first address and a second addressfrom the server when the server cannot accommodate an entry having acorresponding relationship between the first address and the secondaddress which are included in the answer which has been received fromthe one of the plurality of terminals.
 32. A sever comprising: means forreceiving, from an originating terminal, an address interrogationrequest including a first address and a first value indicative of arequest; means for transferring the address information request to aplurality of terminals; means for receiving an answer including a secondvalue indicative of an answer and a second address which corresponds tothe first address from one of the plurality of terminals in response tothe address interrogation request which has been transferred; and meansfor registering, in a memory of the server, a corresponding relationshipbetween the first and the second address in a place designated by anindex value which is calculated based on a value of the first address orthe second address, wherein when the server receives the answerincluding the second address corresponding to the first address from theone of the plurality of terminals, the registration means deletes acorresponding relationship, referred to least recently, when the servercan not accommodate a corresponding relationship between the firstaddress and the second address, and registers the correspondingrelationship between the first address and the second address which isincluded in the answer.
 33. The server according to claim 32, whereinthe terminal address interrogation means diverts terminals into aplurality of groups, interrogates terminals of a first group for asecond address and, when a notification of an answer including a secondaddress is not received within a set period of time, interrogates theterminals of the next group for a second address.
 34. In a networksystem including communication parties accommodated by terminals, amethod of registering a corresponding relationship between a firstidentifier and a second identifier for a communicating party, comprisingthe steps of: when a communication request is issued, determining, in aterminal accommodating an originating party, whether a second identifierfor another communicating party is registered; sending to a server aninterrogation request including a first value indicative of a requestand a first identifier of the other communicating party when the secondidentifier is not registered in the terminal; transferring, by theserver, the interrogation request to a plurality of terminals which canaccommodate the other communicating party when the second identifiercorresponding to the first identifier is not registered in the server;receiving, at the server, an answer including a second value indicativeof an answer and the second identifier which corresponds to the othercommunicating party identified by the first identifier in response tothe interrogation request, said answer from a terminal having it's ownsecond identifier which is not registered in the server; sending theanswer to the terminal accommodating the originating party; andregistering, in the terminal accommodating the originating party, acorresponding relationship between the first identifier and the secondidentifier which is included in the answer.
 35. The method of claim 34wherein the receiving step further includes: registering, in the server,the corresponding relationship between the first identifier and thesecond identifier which is included in the answer.
 36. The method ofclaim 34 wherein when the second identifier corresponding to the firstidentifier is registered in the server, the server responds to theinterrogation request by sending the answer to the terminalaccommodating the originating party.
 37. The method of claim 34 whereinthe plurality of terminals are a plurality of ATM terminals.
 38. Themethod of claim 34 wherein the first identifier is a protocol address.39. The method of claim 34 wherein the second identifier is a terminaladdress.
 40. A network identifier resolution system equipped with aplurality of terminals, a switch or exchange which accommodates eachterminal of a plurality of terminals and a server, wherein: eachterminal of the plurality of terminals comprising: a processor thatreceives a communication request message, determines a first identifierfrom the communication request message, checks a local storage area fora corresponding second identifier, and when a second identifier is notregistered, creates an interrogation request message which includes afirst value indicative of a request and the first identifier; and anetwork interface unit that sends to the server the interrogationrequest message and receives answers and interrogation request messagesfrom the server; the server comprising: a processor that receives theinterrogation request message, checks a storage area for a correspondingsecond identifier, and when a second identifier is not registered,forwards the interrogation request; network interface unit fortransferring the interrogation request message including the first valueindicative of the request and the first identifier to a plurality ofterminals, and receiving, in response to the interrogation requestmessage, an answer including a second identifier corresponding to thefirst identifier from one of the plurality of terminals having it's ownsecond identifier which is not registered in the server; and the storagearea for registering a corresponding relationship between the firstidentifier and the second identifier which has been included in theanswer.
 41. The method of claim 40 wherein a terminal of the pluralityof terminals is a plurality of ATM terminals.
 42. The method of claim 40wherein the first identifier is a protocol address.
 43. The method ofclaim 40 wherein the second identifier is a terminal address.